Get flash to fully experience Pearltrees
A lot of programs, including Freeware, come with various techniques to install additional and most times unwanted software. It is a method for Authors to make some money. Lately, even the better ones do this. CNet.com (download.com) even uses it's own install wrapper to programs that it offers links to. The best advice I can give is to never automatically click through installation buttons without thoroughly investigating each page. Many times, options are included during the installation and you must either opt-out or opt-in.